1. Field of Invention
The present invention relates to data conversion. More particularly, the present invention relates to a digital-to-analog data converter for converting a digital input signal into an analog output current, suitable for data conversion in the devices such as an organic light emitting diode (OLED).
2. Description of Related Art
A digital-to-analog data converter is widely used in, for example, the driver of an organic light emitting diode (OLED) panel, to convert the pixel data received from a digital control circuit into an analog current signal to drive the panel. Moreover, the driver can also employ another two digital-to-analog data converters such that the user can adjust the contrast and luminance of the panel freely.
Flash digital-to-analog data converter can be classified into three modes including voltage-mode, charge-mode and current-mode. The voltage-mode digital-to-analog data converter utilizes the voltages divided by series of resistors to obtain the required analog output value, while the charge-mode digital-to-analog data converter utilizes a plurality of capacitors of different sizes to obtain the required analog output value. However, the outputs of the above two modes are influenced by the precision of the resistors and the capacitors respectively, and a large area is needed for realizing the capacitors on a chip.
Therefore, the current-mode digital-to-analog data converter, such as the segment current-mode digital-to-analog data converter, is commonly used. In the segment current-mode digital-to-analog data converter, a reference current generator is used to generate a constant current, and map it to a plurality of current sources through a current mirror, for example, if the received digital input signal is of (M+L) bits, 2M+L current sources are needed. After that, switches are used to switch these current sources to output the required analog output current.
In more detail, the received digital input signal is first divided into most significant bits having M bits and least significant bits having L bits to be processed respectively. Next, the most significant bits and the least significant bits are decoded by a thermometer decoder respectively, and the decoded signals from the first group of current sources (having 2M current sources) and the second group of current sources (having 2L current sources) are sent to the output node, thereby generating an analog output current corresponding to the digital input signal.
Obviously, the circuit architecture and power consumption of this segment current-mode digital-to-analog data converter will increase along with the bits of the digital input signal increase, and even they will increase in exponential. Therefore, a digital-to-analog data converter having more simple architecture and less power consumption is desired to adapt the increasingly complex circuit architecture.